2009-10-13_REVISION - C1982056 (2)

Home Browse Search

overall CRDA will always slope to the southeast, to prevent drainage over the outslope, and a core- drain and designed perimeter ditches will provide for drainage off of and under the refuse fill. 5. TCC provided cross-sections of the proposed CRDA: A -A and B -B. Cross-Section A A extends from the western extent of the proposed pile through to the eastern extent of the proposed CRDA. Cross-section B-B shows a segment initiating from approximat4ely 50 feet north of the toe of the proposed CRDA expansion and extending roughly 213 of the way through the pile. TCC provided no cross-section depicting the southern end of the CRDA expansion and how the southern extent of the CRDA expansion ties in with the topography on the southern extent. Response: On Sheet C-101, Cross Section B-B has been extended to the south, to the edge of the disturbance area. The extended cross-section indicates that the upper surface of the CRDA intercepts the natural grade at the point where the upper surface terminates at Ditch RDA-1. 6: The CRDA cross-section map shows the proposed refuse elevation and grading at Phase 1, but this map does not show the ditches associated with Phase 1 construction. The ditches should be depicted on the cross-section map too. The CRDA cross-sections map also depicts Phase 2 contours, which are approximately 150 feet lower than the final grade. The text indicates there are two phases, Phase I and final, yet the cross-section map shows Phase 1, Phase 2 and final contours Please explain the phases of pile construction. Response: Please refer to the previous response to Comment 4. Temporary diversion ditches will be constructed and maintained a maximum of 50 vertical feet above the refuse pile to control surface drainage between the permanent ditch and the southern limit of the refuse pile. Soil and cover material stripping will occur at the same time as ditch construction to maintain an adequate buffer zone. The cross-sections have been revised to show their intersection with the designed ditches and phasing designations have been eliminated as confusing and not representative of the anticipated CRDA Expansion activities (only initial construction and full build-out configurations are now shown). 7. Exhibit 26C indicates that a minimum of 2 piezometer wells be installed in the CRDA expansion to monitor water within the pile. The maps do not show where these piezometers will be placed nor is there any discussion regarding how the piezometers will be constructed or frequency of monitoring. A description of number of piezometers, location of piezometers, construction methods, construction timing, monitoring methods and frequency needs to be included in the discussion. Response: Review of monitoring considerations has resulted in the decision to install three piezometers, at the locations shown on revised Drawing C-101. When refuse placement reaches the full bench height at the designated monitoring sites, geotech test holes will be drilled through the coal refuse materials, and a minimum of 5 feet into the underlying spoils with a drill rig utilizing 4-inch diameter continuous-flight power augers. The test holes will be cased with slotted, 2.0-inch diameter Schedule-40 PVC pipe so that water levels within the CRDA and foundation materials can be monitored. The PVC casing will extend within approximately 3 feet of the CRDA bench surface, and_a solid 2- inch diameter PVC pipe riser will be placed over the slotted pipe, extending approximately 3 feet above the surface of the CRDA bench. Free draining sand will be placed around the slotted pipe to within 3 feet of the ground surface. A well seal will be placed over the sand pack using bentonite pellets and/ or chips. A protective steel casing with a lockable lid will be placed over the completed piezometer to provide protection from impact. Piezometers will be monitored monthly and the results